DE102005032591B4 - Doped iridium with improved high temperature properties - Google Patents

Abstract

The invention relates to an iridium alloy of at least 85% by weight iridium, at least 0.005% by weight molybdenum, 0.001 to 0.6% by weight hafnium and, if necessary, rhenium, the sum of molybdenum and hafnium being between 0.02 and 1.2% by weight, and to a process for the production of an iridium alloy, an IrMo and an IrHf master alloy, respectively, being produced in the electric arc and immersed into an iridium melt, if necessary together with Re.

Description

The present invention relates to the doping of iridium or iridium-rhenium alloy with molybdenum and hafnium.

WO 2004/007782 is one of many uses of Iridium crucible for crystal growth. It describes tungsten and / or zirconium-containing iridium alloys which additionally contain 0.01 to 0.5 wt .-% of other elements such as molybdenum and hafnium and optionally contain ruthenium at 0.01 to 10 wt .-%. It is also mentioned in this document that the addition of these additional elements alone is not effective.

US 4,444,728 describes iridium-rhenium crucibles with 1 to 15 wt .-% rhenium.

To US 3,918,965 The mechanical properties of iridium are greatly improved by doping with 0.65 to 0.93 wt .-% hafnium.

The object of the present invention is to increase the creep and creep rupture strength based on the excellent corrosion resistance of the iridium to oxidic melts, to improve the behavior under mechanical stress, and to reduce the coarse grain formation in the recrystallization.

This object is achieved with the features of claim 1.

Preferred embodiments and applications are described in the following claims.

To increase the creep rupture strength at 1800 ° C., a doping of iridium or iridium-rhenium alloy is carried out with at least 50 ppm molybdenum and at least 5 ppm hafnium, the sum of molybdenum and hafnium being between 200 ppm and 1.2% by weight, in particular between 0.02 and 0.7 wt%.

In a preferred embodiment, the proportion of molybdenum 0.01 to 0.8 wt .-%, in particular 0.02 to 0.3 wt .-% molybdenum; and the proportion of hafnium 0.001 to 0.4 wt .-%, in particular 0.01 to 0.2 wt .-% hafnium. As a result, the coarse grain formation during recrystallization slowed noticeably and increases the creep and creep strength. This doped iridium shows compared to oxidic melts significantly improved behavior under mechanical stress. The same components cause iridium-rhenium alloys having at least 85 wt .-% Ir, preferably with up to 8 wt .-% rhenium, in particular 0.1 to 5 wt .-% Re, even more effective results in terms of reduced coarse grain formation by recrystallization , and high-temperature strength. In addition, the tendency to cavitation is significantly reduced.

In a further preferred embodiment, the weight ratio of molybdenum to hafnium is between 3: 1 and 1: 1, in particular between 2.5: 1 and 1.5: 1.

For the production of alloys according to the invention, it has proven useful to produce IrMo and IrHf master alloys in the arc. These master alloys are introduced in relation to the target alloy in an iridium melt or doused by an iridium melt. In addition, Re can be introduced into the Ir melt.

• 1. Mit 0,05 Gew.-% Molybdän dotiertes Iridium wird durch Dotierung mit 0,001 Gew.-% Hafnium hinsichtlich der Zeitstandfestigkeit bei 1800°C verbessert. Diese Verbesserung tritt bei einer Dotierung mit Hf zwischen 0,01 und 0,1 Gew.-% am deutlichsten auf. Bei einer Dotierung über 0,5 Gew.-% Hf wird die Verarbeitbarkeit der Legierung schwieriger.
• 2. Ein mit 0,3 Gew.-% Hafnium dotiertes Iridium zeigt eine Erhöhung der Zeitstandfestigkeit bei 1800°C durch Dotierung mit 0,01 Gew.-% Molybdän. Die Zeitstandfestigkeit wird weiter deutlich verbessert durch Dotierung mit Mo in einem Bereich zwischen 0,02 und 0,3 Gew.-%. Bei einer Dotierung über 0,8 Gew.-% Mo wird die Verarbeitbarkeit der Legierung schwieriger.
• 3. Nimmt man in den zuvor beschriebenen Beispielen statt Iridium eine Iridium-Rhenium-Legierung mit 0,1 Gew.-% Rhenium, 1 Gew.-% Rhenium und 8 Gew.-% Rhenium, so ist eine weitere Steigerung der Hochtemperaturfestigkeit bei gleichzeitiger Reduzierung der Neigung zur Lunkerbildung festzustellen, wobei mit 1 Gew.-% Rhenium die besten Ergebnisse erzielt wurden. Bei einer Dotierung über 8 Gew.-% Rhenium wird die Verarbeitbarkeit der Legierung schwierig.

The invention is illustrated below with reference to examples.

• 1. Iridium doped with 0.05% by weight molybdenum is improved by doping with 0.001% by weight hafnium with respect to the creep rupture strength at 1800 ° C. This improvement is most pronounced in the case of doping with Hf between 0.01 and 0.1% by weight. At a doping above 0.5 wt% Hf, the processability of the alloy becomes more difficult.
• 2. An iridium doped with 0.3% by weight of hafnium shows an increase in the creep rupture strength at 1800 ° C. by doping with 0.01% by weight of molybdenum. The creep strength is further significantly improved by doping with Mo in a range between 0.02 and 0.3 wt .-%. At a doping above 0.8 wt% Mo, the processability of the alloy becomes more difficult.
• 3. Taking in the examples described above iridium instead of an iridium-rhenium alloy with 0.1 wt .-% rhenium, 1 wt .-% rhenium and 8 wt .-% rhenium, so is a further increase in high-temperature strength at the same time Reduction of the tendency to cavitation, with 1 wt .-% rhenium, the best results were achieved. With a doping above 8% by weight of rhenium, the processability of the alloy becomes difficult.

EXAMPLES

Inventive iridium alloys are obtainable by remelting master alloys with Ir. An Ir Hf 1 and an Ir Mo 1 master alloy are produced in the arc.

• – einwiegen von 99 g Ir und 1 g Hf
• – chargieren in eine wassergekühlte Cu-Kokille
• – evakuieren
• – 300 mbar Argon fluten
• – Lichtbogen zünden und die Legierung aufschmelzen
• – mehrmals umschmelzen, um eine homogene Legierung zu erhalten

This is followed by a melting process in an arc system with W electrode

• Weigh out 99 g Ir and 1 g Hf
• - Charge into a water-cooled copper mold
• - evacuate
• - 300 mbar argon flood
• - ignite the arc and melt the alloy
• - remelt several times to obtain a homogeneous alloy

For Ir Mo 1, the process is repeated accordingly.

If necessary, during the manufacturing process of the alloy melt, Re is added and the two master alloys are immersed in the Ir melt in order to prevent oxidation of the alloy constituents. For this purpose, the master alloys are guided with a rod of zirconium oxide in the Iridiumschmelze and kept against surfacing.

3 kg of an alloy of Ir - 1% Re - 0.04% Mo - 0.02% Hf was inductively melted under argon atmosphere and poured into a copper mold 20 mm × 70 mm × 100 mm according to standard practice. Noticeable in the billet was the lower voids formation, as is usually observed with pure iridium. The ingot was hot forged according to normal practice and hot rolled to a thickness of 1 mm, being heated to 1400 ° C before each rolling pass. In hot forming, the alloy behaved similarly to pure iridium. Similar to the pure iridium, a final annealing was carried out after the shaping for 20 minutes / 1400 ° C. A metallographic ground investigation showed a uniformly recrystallized microstructure with a mean particle size of 0.095 mm.

From this alloyed Ir sheet, a sample was cut and aged at 1400 ° C for 100 hours. In metallographic grinding, a uniformly recrystallized microstructure with an average particle size of 0.11 mm was found.

From the same alloyed Ir sheet 3 samples were cut for creep tests. These samples were tested at 1800 ° C under a load of 16.9 MPa, corresponding to the load that gave a lifetime of 10.0 hours for pure iridium, under an Ar / H2 95/5 atmosphere. The time to break of each sample was 15.4; 16.6 or 18.8 hours.

Another ingot of the same alloy composition was melted and formed into a 2.4 mm thick sheet. From this sheet, a cylindrical crucible having an outer diameter of 50 mm and a height of 60 mm was produced by hot-drawing. During the transformation, the alloy behaved analogously to pure Ir.

Using this crucible, a single crystal of neodymium-yttrium-aluminum garnet was grown by the Czochralski method.

In an analogous manner, a billet made of the alloy Ir - 0.3% Mo - 0.04% Hf was melted, cast and formed into a 1 mm sheet. After final annealing, the sheet had a uniformly recrystallized microstructure with a mean grain size of 0.3 mm.

After an additional sample annealing for 100 hours at 1400 ° C, a uniformly recrystallized microstructure with a mean grain size of 0.6 mm was found.

In the creep test at 1800 ° C under a load of 16.9 MPa were on 3 samples lives of 12.0; Measured 12.6 and 13.1 hours, respectively.

In an analogous manner, a billet made of the alloy Ir - 3% Re - 0.05% Mo - 0.03% Hf was melted, cast and formed into a 1 mm sheet. After the final annealing, the sheet had a uniformly recrystallized microstructure with a mean grain size of 0.075 mm.

After an additional sample annealing for 100 hours at 1400 ° C, a uniformly recrystallized microstructure with a mean particle size of 0.09 mm was found.

In the creep test at 1800 ° C under a load of 16.9 MPa, service lives of 18.1; Measured 19.7 and 20.9 hours, respectively.

Another ingot of the same alloy composition was melted and formed into a 2.4 mm thick sheet. From this sheet, a cylindrical crucible having an outer diameter of 30 mm and a height of 35 mm was produced by hot-drawing. The forming required a higher force application than pure iridium. Likewise, the crucible had to be subjected more frequently to an intermediate annealing (10 minutes / 1400 ° C.) than usual for pure iridium. Otherwise, the transformation was flawless. Using this crucible, a single crystal of sapphire was melted from an alumina melt by the Czochralski method.

Comparative Examples:

A sample of a 1 mm thick sheet of pure iridium was examined after rolling and final annealing for 20 minutes / 1400 ° C in metallographic grinding. The sample showed a uniformly recrystallized microstructure with a mean grain size of 0.7 mm.

Another sample of the same Ir sheet was aged for a further 100 hours at 1400 ° C after final annealing and examined by metallography. The sample showed a recrystallized microstructure with partial coarse grain formation. The grain size was unevenly between 1 and 2 mm.

Ten samples of the same Ir sheet were subjected to final annealing under various loads between 6 and 25 MPa at 1800 ° C under an Ar / H2 95/5 atmosphere and the time to break each sample was determined. For a load of 16.9 MPa, a service life of 10.0 hours until breakage was determined.

Claims (5)

An alloy containing at least 0.005% by weight of molybdenum and 0.0005 to 0.6% by weight of hafnium, the sum of molybdenum and hafnium being between 0.02 and 1.2% by weight, optionally rhenium, and the remainder at least 85% by weight iridium. An alloy according to claim 1, characterized by 0.01 to 0.8 wt .-% molybdenum and 0.002 to 0.4 wt .-% hafnium and optionally up to 8 wt .-% rhenium. Alloy according to claim 1 or 2, characterized in that it comprises 0.1 to 5% by weight of rhenium. Alloy according to one of Claims 1 to 3, characterized in that it contains 0.02 to 0.3% by weight of molybdenum. Alloy according to one of claims 1 to 4, characterized in that it comprises 0.002 to 0.2% by weight of hafnium.